Afon Cefni is one of the major

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

s on the island of

Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey island ...

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. It is long. Its source is near to the village of Capel Coch, before flowing through

Bodffordd Bodffordd () is a village and community in central Anglesey, Wales. As of the 2011 census, the community's population was 960. The community includes the hamlets of Trefor, Heneglwys and Bodwrog. Description and history Bodffordd is located ...

and into Llyn Cefni in the centre of the island. It continues to run south through the county town of Llangefni. Just north of the A55 the river turns and flows south-west. It passes through the flatlands of the

Malltraeth Marsh Malltraeth Marsh (also spelled as Malldraeth; cy, Cors Malltraeth or cy, Cors Ddyga, label=none) is a large marsh area in Anglesey, North Wales, north-east of Malltraeth village, along the flatlands of Trefdraeth, Bodorgan, Llangristiolus ...

es, where the river course was altered in 1824, creating a canal-like straight stretch. This part of the river and the surrounding marshes, part of which is a RSPB reserve, are frequented by a variety of wetland birds which in their turn are preyed on by falcons, hawks and harriers. A cycle trail follows the straightened course of the river as it flows through the marshes. Finally it flows under a bridge carrying the North Wales Coast Railway Line at Malltraeth Sands in the south-west of the island and into the

Irish Sea The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the C ...

. The viaduct is described as "noble" and has nineteen arches. An embankment carries the

A4080 The A4080 is a British A road which is located on the Island of Anglesey, Wales. It follows a very roundabout route from the A5 road at Llanfairpwllgwyngyll via Newborough and Rhosneigr back to the A55 and the A5 about south of Holyhead. ...

across the estuary at the village of

Malltraeth Malltraeth (origin: ''Mall'' (corrupt, blasted, desolate, + ''Traeth'' (beach))) is a small village in the southwest of Anglesey, in the community of Bodorgan. It is now at the end of a large bay, which used to extend much further inland, alm ...

, half a mile below the railway bridge. Another RSPB reserve is to be found in the estuary here, Newbourough Warren. Malltraeth Pool at the north end of the estuary is a place visited by many waterbirds during their spring and autumn migrations, and other wildfowl and waders are to be seen on the estuary all winter. Newborough Forest on the southern shore is used by large numbers of

raven A raven is any of several larger-bodied bird species of the genus '' Corvus''. These species do not form a single taxonomic group within the genus. There is no consistent distinction between " crows" and "ravens", common names which are assigne ...

s as a winter roost, and a peninsula and a rocky islet in the estuary are a breeding ground for shags and

cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven ge ...

s. Migration of fish and eels is effectively blocked by the dam at the Cefni water treatment works, holding back the Cefni reservoir. Attempts to prompt the installation of a fish pass have proven unsuccessful to date. There was a ship named after the river built in Glasgow in 1890 by a company based in Menai Bridge. There is currently a tug named ''Afon Cefni'', operated by Holyhead Towing. It can be tracked on Ship AIS websites.

References

{{Authority control Rivers of Anglesey